Metal to glass sealing fixture



Dec. 25, 1956 J. K. McDUFFr-:E 2,775,068

METAL TO GLASS SEALINGAFIXTURE Filed March 22, 1954 WAX United StatesPatent O METAL TO GLASS SEALING FIXTURE John K. McDulfee, Kutztown, Pa.,assignor to Western Electric Company, Incorporated, New York, N. Y., acorporation of New York Application March 22, 1954, Serial No. 417,685

Claims. (Cl. 49-1) This invention relates to apparatus for sealing glassto metal and particularly to a fixture for accurately positioning andfusing together a plurality of glass and metal parts.

In the manufacture of electron discharge devices currently employed inhigh frequency communication apparatus, it is essential that the variousmetal and glass parts thereof be accurately assembled and fused since,due to the very short wave length of the frequencies involved, anyslight misalignment of parts or electrodes supported by the parts maymake the devices inoperative.

It is therefore, the prinicipal object of this invention to facilitatethe fabrication of such devices while insuring accurate spacialrelationship between the parts.

In accordance with the general features of the invention, a mandrel isprovided which is movable between a loading position, where it may beloaded with the glass and metal parts, and a heating position in achamber where the parts are fused. Means are provided for concentricallyaligning the parts at the loading position and at least one contouredforming tool on a movable rod is utilized to apply pressure to theassembled parts to compress them to predetermined spacial relationshipalong the mandrel when the parts are heated within the field of aninduction coil provided in the chamber.

According to an important feature of the invention, the mandrel ishollow and gas under pressure is applied thereto, to produce an internalpressure to the assembled parts to prevent the glass seals fromshrinking inwardly as the glass becomes plastic.

Other features of the invention will be more fully understood from thefollowing detailed description taken in conjunction with theaccompanying drawings, in which:

Fig. 1 is a front, partially broken, elevational view of a fixtureaccording to the invention;

Fig. 2 is an exploded view of the metal and glass parts of a vacuum tubethat are fused together by the fixture shown in Fig. l;

Fig. 3 is a detailed view of the parts to be fused posil tioned inheating position in the fixture;

Fig. 4 is a partially broken View showing the details of the partsreceiving member of the mandrel with a fused bulb assembly mountedthereon, and

Fig. 5 is an isometric view of the parts locating members of thefixture.

Referring now to the drawing, the fixture shown is designedforfabricating the bulb assembly of a Western Electric Co. type 416A triodevacuum tube, designed for high frequency use, which is similar to thatdisclosed in Patent 2,527,127 issued October 24, 1950, to R. S. Gormley,C. Maggs and L. F. Moose. This bulb assembly comprises a pre-fused anodeterminal seal assembly which includes the glass support seal 5 and themetal anode terminal 6, a metal grid terminal ring 7, a glass ring 8 anda metal bulb 9.

As seen in Fig. l, a main support structure 10 is provided for a closedoven 13, a lower, vertically slidable mandrel 11, two upper, verticallyslidable rods 14 and 15 2,775,068 Patented Dec. 25, 1956 ICC and twohorizontally slidable locating members 16 and 17. The mandrel 11 has acontoured parts receiving member 12 attached to its upper end which isprovided with parallel, annular plane surfaces 53, 19 and 26 (Fig. 4)inaccurate spacial relationship for precisely locating the anode terminal6, grid terminal ring 7 and bulb 9 respectively, along the vertical axis54-54 of the member 12 when the assembled parts are compressed thereonwhile fusing. Concentric, cylindrical portions 21, 20 and 18, havingdiameters slightly less than an internal, axial hole in the anodeterminal 6, annular ring 50 of the grid terminal ring 7 and the internaldiameter 49 of the bulb respectively, insure proper co-axial alignmentof the parts. The glass ring 8 is aligned co-axially by the rib 39 oflocating member 48 (Fig. 5) while in loading position. This will be morefully described in the operation of the device which is discussed below.

The mandrel 11 is movable so that it may occupy a loading position, asshown, where the lower portion of member 12 is supported on fixed sleeve27 for the mandrel or the mandrel may be raised to a heating positionwhere the upper portion of member 12 is inserted into the oven 13. Alocking member 25, pivotally mounted to the base 34 of the mainstructure 10, is provided for engaging a lower end member 28 to lock themandrel 11 in the raised position as shown by the dotted lines in Fig. lwhere the bulb assembly will occupy the position shown in Fig. 3. Anaxial hole 33 in the mandrel 11 is provided for applying gas, underpressure, from a source not shown, through tube 29 to holes 30 in member12. This is provided for blowing the glass seals and will be describedmore fully below.

Rod 14 is slip fitted in a central axial hole provided in rod 15, ananode terminal receiving hole 35 being provided in the lower end of rod14. Rod 15, which is slip fitted in fixed sleeves or bearings 22 and 23,has a contoured grid terminal ring contacting member 24 for engaging thetop iiange of the grid terminal ring 7. A spring stop member 36, mountedto the top of the main structure 10, is adapted to engage annular weightmember 37 fixed to the top of rod 14 to secure the rod in a normallyraised position.

Locating members 16 and 17 are slidably mounted in fixed sleeves 37 and38 respectively and are provided with split centering clamps 48 foraligning the various parts assembled on the mandrel member 12. A raisedsemiannular ridge 39 is provided on the inner semi-cylindrical surfaceof the clamps 48 for concentrically positioning the glass ring 8 withrespect to the other parts. The members 16 and 17 are prevented fromtwisting out of proper orientation by dowel pins 40 which are mounted inhandles 41 and 42 and which slide in holes 43 in the fixed sleeves 37and 38.

The oven 13 is a closed b'ox having an induction heating coil 44 mountedtherein for heating the parts when mandrel 11 is in its raised position,a hole 45 being provided in Ithe bottom panel of the oven to allow themandrel member 12 to pass therein. An opening is also provided in thetop of the oven through which rods 14 and 15 may be moved. Water coolingcoils 46 are mounted on the walls of the oven to prevent distortion ofthe fixture through overheating.

Operation By removing the locking member 25 from engagement with themandrel end member 28, the mandrel will, of its own weight, drop toloading position as shown in Fig. l. In this position, the parts areplaced on the mandrel member 12 in the following order: first, theoxidized metal bulb 9, the lower flange of which will rest on the iiatannular surface 26, then the glass ring 8, the oxidized metal gridterminal ring 7 and finally the pre-fused anode termimandrel is in theheating position, means for introducing an inert atmosphere into thechamber, at least one rod extending down into the chamber having acontoured, parts contacting end for subjecting the parts to compressivepressure to position them on the respective parts locating means alongthe parts receiving means, and means for introducing an inert gas underpressure into the hole in the mandrel for blowing the glass seals toprevent them from shrinking inwardly.

References Cited in the le of this patent UNITED STATES PATENTS MillerFeb. 3, 1942 Greiner Jan. 17, 1950 Haas June 20, 1950 Vinson May l, 1951Clark et al May 22, 1951 Haas Nov, 20, 1951

